In electrophotography, an image copy can be obtained by developing electrostatically charged images formed on a photoreceptor with resin powders generally containing pigments (hereinafter "toners") to visualize the images and transferring the visual images onto a duplicating paper, followed by fixing the resulting images thereon. The photoreceptor is, thereafter, required to undergo cleaning before forming electrostatically charged images again. Such a cleaning process is important, because incomplete and ineffective cleaning will often lead to deterioration of images over time.
Therefore, many approaches have been proposed to facilitate the cleaning process, such as a method which comprises preventing toners from adherence to the photoreceptor by providing lubricating agents on the surface of a photoreceptor, a method which comprises adding inorganic fine particles such as silica or alumina in toners themselves to prevent toners from direct contact with the photoreceptor, a method which comprises preventing toners from adherence by suitably abrading the photoreceptor or a method which comprises adding lubricating agents of metal salts of a fatty acid to toners externally.
However, when inorganic fine particles are added to toners and the surface layer of a photoreceptor is composed of organic substances, the surface of the photoreceptor is likely to cave or to be scratched by hard inorganic fine powders, and the abrasive effects obtained when a surface layer of a photoreceptor is composed of inorganic substances cannot be obtained. Therefore, toners are liable to partially adhere at the scratched areas. Further, even when toners are not firmly adhered to the photoreceptor surface, cleaning effects are likely to decrease with the passage of time, leading to the deterioration of images. Such a decrease of cleaning effects is particularly prominent when a two-component type developer using hard carriers is used. cl SUMMARY OF THE INVENTION
An object of the present invention is to solve the above described problems.
That is, a first object of the present invention is to provide a toner composition capable of developing electrostatically charged images which hardly adhere on the surface of a photoreceptor comprising organic substances.
A second object of the present invention is to provide a toner composition for a two-component type developer which can be easily and uniformly cleaned from the photoreceptor surface layer comprising organic substances without causing deterioration of images.
A third object of the present invention is to provide a toner composition for a two-component type developer which does not cause deterioration of a photoreceptor having a surface layer comprising organic substances.
The above and other objects of the present invention can be attained by adding a powder of a fatty acid bisamide compound to the toners as an external additive.